Equipment having an actuator, such as a hydraulic cylinder, is equipped with a filter device for filtering fluid such as operating oil that circulates in a hydraulic circuit. The filter device is provided with a housing, and a filter element which filters the fluid that is to be filtered, and which is contained within the housing.
When a filter device is used beyond a certain period of time, the performance of the filter element degrades due to clogging and the like, and the filter element is therefore replaced.
The housing is provided with a drain valve for discharging the operating oil from the housing. When opening the housing, for example, when replacing the filter element, first, the operating oil is discharged from the housing by opening the drain valve.
This type of drain valve is formed in the housing, and is held in a hole which communicates between the inner side and the outer side of the housing.